pick_first weighted shuffle (1.79.x backport) #12634
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Previously, the number of endpoints in a locality would skew how much traffic was sent to that locality. Also, if endpoints in localities had wildly different weights, that would impact cross-locality weighting. For example, consider: LocalityA weight=1 endpointWeights=[100, 100, 100, 100] LocalityB weight=1 endpointWeights=[1] The endpoint in LocalityB should have an endpoint weight that is half the total sum of endpoint weights, in order to receive half the traffic. But the multiple endpoints in LocalityA would cause it to get 4x the traffic and the endpoint weights in LocalityA causes them to get 100x the traffic. See gRFC A113
kannanjgithub
approved these changes
Jan 28, 2026
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There's two commits here with descriptions in each; take a look at each individually and I'll keep them separate when merging.
There will be a gRFC for this, but apparently it hasn't been created yet(gRFC A113 grpc/proposal#535) and I didn't want to wait longer for it to be created before starting review, because the plan is to delay the 1.79.0 release for this in Java and Go. We will want to merge this ASAP (and backport at our convenience), but we must wait until the gRFC is merged before publishing the 1.79.0 release. I suggest we leaveTODO:release blockerlabel here until the gRFC is merged. (Kannan, I shared a doc and an email thread with you to give you some context; mostly for what problem is being solved, and not the specific solution here. The specific solution here is split across a lot of comments, so you're best off waiting for the gRFC to see something documenting it.)While doing this I've noticed lots of things to fix with how weights are handled. I've basically ignored them at the moment, only trying to make sure that I don't make things worse. I'll be doing a follow-up to fix more weight handling, but I will not be trying to backport it.
Backport of #12623